Three weeks ago, Jennifer Dunn got a new neighbor. She had lived in her duplex apartment in Oak Creek, Wis., for nearly a year when her landlord, Kurt Weins, informed her he had rented out the space upstairs. Her new neighbor showed up with his belongings packed into two large garbage bags. His name was Wade Michael Page.

Last weekend, Page left a path of destruction at the sprawling Sikh temple — or gurdwara — in the Milwaukee suburb, leaving six dead before the gunman killed himself. Dunn, a psychiatric nurse, wonders if things would have turned out differently if she had engaged him more and seen enough to warrant calling in help.

As it was, Dunn barely saw Page during his brief tenancy. Her neighbor rarely stepped outside. She never really heard a sound from above. Occasionally, while she played in the backyard with her six-month-old black lab puppy, Dunn would see Page come out of his apartment and head to his truck parked near the alley. The hulking man with the close-cropped haircut rarely looked her in the eye, though he’d sometimes grunt a greeting before going on his way. Though the landlord told her he worked late shifts, Dunn never figured out what job he did, if any; meanwhile, she estimates that Page’s truck was parked at the home 80% to 90% of the time.

Her landlord, Dunn says, had told her that the new tenant would be no trouble. Indeed, she says, the owner had rented out a room in his own home to Page when the man answered an ad for a spare room. Page apparently kept quietly to himself there until Page asked to rent the upper duplex apartment the landlord also owned across the street.

And then the quiet, nearly invisible neighbor suddenly got a bit more noticeable. Last Friday night, two days before the killing spree, Dunn heard loud “thumping music” coming from his apartment. She decided to tolerate it as long as the music (“indistinguishable but heavy,” she recalls) ended before her kids needed to go to bed. It did.

On Saturday, Dunn noticed Page was up unusually early, at about 5 a.m. Later that morning, Dunn was in the backyard with her daughter. “He had the same two garbage bags I saw him move in with. I never saw him move in anything other than that. I assume he did.” Dunn’s daughter came in to tell her the neighbor was “acting weird.” He had set a cardboard box in the front seat of his truck, and had begun pacing back and forth for several minutes. When Dunn went outside to have a look, he had already left.

The next day Dunn’s daughter asked, “Hey, Mom, did you know there was a shooting?”

Dunn would hear some of the initial details on her car radio as she drove to work. But it wasn’t until she received a call at work from the Milwaukee district attorney assuring her that her children and dog had been evacuated and were safe, that she realized her neighbor was involved. Dunn and her girls were not to return to their apartment until 11 o’ clock that evening. “It was very important to get back into the house for the girls to know it was safe, to sleep in their own beds.”

Later, Dunn had a peek at the killer’s apartment. It was scarcely furnished. “It had a mattress, remnants of the computer setup and a TV that he left,” she tells TIME. “The refrigerator was as clean as the last tenants left it. There was weird stuff left all over the stove.”

Dunn desperately wants to feel safe again. “It’s a really nice community,” she says. “Up until all this happened, I felt really safe. It’s got a big backyard for them to play in, along with the dog. Work’s not that far away.” But she admits, “I’m not sleeping. I’m trying to figure out how I’m going to get out of here.” Though she works with psychiatric patients in the behavioral unit of a hospital, her brief exposure to Page didn’t raise flags. “I work in a long-term residential unit with folks that cannot live in the community. I’m used to physically aggressive patients, pedophiles, people with developmental disabilities … There are certain behaviors that you cue in on. He didn’t have these behaviors.”

The “what ifs” bother her. “This is the only time in my life that I paid attention to my skin color,” she says. “What if I wasn’t white? What if I had a friend over who wasn’t white? Would he have been offended? I deal with mental illness all the time, and I understand the complexity of it. It’s very unfortunate he wasn’t in a situation where he was helped with whatever his issues were.”

And then Dunn’s thoughts turn to the Sikh community that lost six members, with two still recovering from their injuries. “What I’m going through is nothing compared to what [the Sikhs] are going through.” Like the Sikh community, Dunn is hopeful some good will come out of this mass killing. She yearns for the friends and families of the victims to reach a sense of peace. “My hope is that someone digs into why he did what he did, to see if it was mental illness. That puts the spotlight on it and educates people. It shows what can happen if it goes untreated.”